An aide told NBC News that Dole should be discharged tomorrow

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Dole, 89, ran for president against Bill Clinton in 1996 and was the Republican vice presidential nominee in 1976.

Updated at 3:22 AM PST on Wednesday, Nov 28, 2012

Sen. Bob Dole has been admitted to Walter Reed Army medical center for what one of his aide's called a "routine procedure."

"Senator Dole self checked into the hospital for a routine procedure and will be discharged tomorrow," an aide told NBC News. "He's doing very well."

Earlier Tuesday, Senate Majority Leader Harry Reid said on the Senate floor that Dole was hospitalized "because he is infirm."

The comment came during a debate on the ratification of the Convention on the Rights of Persons with Disabilities, an international treaty aimed at addressing disability rights. Sen. John McCain, according to NBC News, explained that Bob Dole, a proponent of the treaty, had sent an email yesterday requesting support for the CRPD and indicating that he was hospitalized and therefore forced to email rather than call.

"I freely admit that I love Bob Dole, I listen to him, I appreciate his leadership. I think the Majority Leader would agree that we appreciate his bipartisanship during a great deal of his time," McCain told his colleagues, according to NBC News. "I hope my colleagues would, before deciding to vote, at least listen to the letter that was addressed to all of us by Senator Bob Dole."

After McCain read the note, which touted the treaty, Reid added that he had recently heard from Dole.

"He called me a few days ago," McCain said, according to NBC News. "He's at Walter Reid for a checkup; he's there because he's infirm ... and he's sick. We should do this for many many reasons, not the least of which is to recognize what a great leader Bob Dole is and has been for our country."

A colleague of Dole told NBC News, however, that the former presidential nominee was hospitalized for a "relatively minor procedure" and that he watched the Senate floor debate from his room. The colleague added that if Dole feels up to it, he is expected to speak Thursday at a Senate tribute to the late Sen. Warren Rudman.

Dole, 89, ran for president against Bill Clinton in 1996 and was the Republican vice presidential nominee in 1976.